Move start up, Static Difference (frame advantage), Starting Proration, Proration Multiplier.
For more info see http://dustloop.com/guides/bbcs/systemGuide/systemGuide.html
Ragna's backdash can aways evade the steel rain if done as soon as possible.
I guess the only exceptions are when he is doing a forward dash or recovering from something.
By back dashing he wouldn't be forced to block anything, and by dashing then back throwing, the mix up would surely not be guaranteed.
At least not like it was in that match.
Are you referring to 1:05 of this match ?
Because Kaqn could have escaped that by just back dashing, or back throwing and then barrier blocking the nails.